To troubleshoot and diagnose a gas range, you must first understand the principles of operation. The components that make up a gas oven ignition system are, the igniter, sometimes referred to as the glow bar because it always glows red when it is operating, the oven safety valve, the oven burner tube, and the oven thermostat, or electronic control.
The Gas Oven Ignitor
Gas oven igniters are made of a carbon based material that can withstand a tremendous amount of heat. First off, an oven igniter must glow red hot to ignite the gas flame, then it must remain on and red hot the whole time the gas burner is on. The oven ignitor will be mounted in close proximity to the oven burner. This will allow the gas to ignite as soon as it starts to flow. Gas oven igniters are not interchangeable. A gas oven igniter is matched to the current draw of the safety valve in the system.
The Gas Oven Safety Valve
The safety valve usually sits flat on the oven base. It is connected on one end to a gas line attached to the gas supply pressure regulator. The other end of the safety valve is the outlet that allows gas to flow into the oven burner assembly. Within the oven safety valve is a bimetallic lever that is attached to a plunger that moves back and forth to let the gas flow. The bimetallic lever is connected to terminals that stick out of the top of the oven safety valve.
The Oven Burner Assembly
The oven burner assembly is usually mounted from front to back beneath the floor of the oven. It has specific size holes to regulate the gas flame. On top of the oven burner assembly you will find a heavy-duty plate, called a flame spreader. The flame spreader is designed to evenly distribute the heat to the left and right side of the oven cavity.
How These Components Work Together
When the oven is first turned on, the heat circuit is complete through the oven thermostat, or relay on an electronic control, through one end of the igniter. The current passes through the ignitor, out the other side, and into one of the terminals on the safety valve. The other side of the safety valve is usually connected to the neutral side of the electrical supply line. So now we have a completed circuit through the thermostat or electronic control through the igniter and through the oven safety valve. As the igniter starts to glow and heat up, it's resistance will decrease.
As the resistance of the igniter decreases, it will start to draw more current through the line. As the current passes through the circuit it must pass through the bimetallic strip within the oven safety valve. When this happens the bimetal strip starts to heat up and flex. By this time now the oven ignitor is glowing red hot. As the bimetal in the oven safety valve flexes, it opens the plunger allowing gas to flow to the oven burner. And since the igniter is glowing red hot, the gas will ignite. Current will continue to flow through the oven igniter safety valve and thermostat, or electronic control relay, until the oven reaches the selected temperature. At that time the thermostat, or electronic control, will open the circuit to the igniter. When there is no longer current passing through the igniter, the bimetallic strip within the oven safety valve cools down. When that happens, it flexes back to the closed position and shuts off the gas to the burner assembly.
If you have a gas oven that will not ignite, and the igniter is glowing red, you need to check the current draw of the igniter. Because it is glowing red you know that the circuit is complete through the igniter, through the oven safety valve, through the oven thermostat or electronic control relay, in and out of any safety fuses or high temp thermostats used as safety devices, and on out to the neutral side of the supply line. Therefore you do not need to check any of those components. Oven safety valves have a specific electrical current rating. That current rating is usually stamped on the side of the oven safety valve. When you have an igniter that is glowing red, but the oven still will not light, a high percentage of the time the problem is the fact that the igniter resistance has increased and it's not drawing enough current to flex the bimetallic strip in the oven safety valve. An amp probe on the line cord is used to check the current draw of a gas range. Most of the time you'll find that if an igniter is glowing red, and the oven is not lighting, the current draw of the ignitor will be low and it is likely defective.